Gel assisted separation method and dewatering/desalting hydrocarbon oils

ABSTRACT

A method for separating polar hydrocarbon compounds from a hydrocarbon oil containing polar hydrocarbon compounds comprising the steps of: a) forming a gel in the hydrocarbon oil, and thereafter b) separating the gel from the hydrocarbon oil to produce a separated gel and a separated hydrocarbon oil.

FIELD OF THE INVENTION

This application claims the benefit of U.S. Provisional Application60/590,891 filed Jul. 23, 2004.

The invention relates to separating polar hydrocarbons from hydrocarbonoils. The invention also relates to desalting and/or dewateringhydrocarbon oils.

BACKGROUND

Hydrocarbon oils, particularly heavy crude oils, contain polarhydrocarbon compounds such as naphthenic acids, nitrogen and sulfurcontaining hydrocarbon compounds and pose problems in refining. There isa need to upgrade such hydrocrabon oils. Separation of polar hydrocarboncompounds such as naphthenic acids, nitrogen and sulfur containinghydrocarbon compounds from crude oils results in upgrading. The presentinvention addresses this need.

Hydrocarbon oils, particularly crude oils when produced comprise varyingamounts of water and inorganic salts like halogens, sulfates andcarbonates of Group I and Group II elements of The Periodic Table ofElements. (The Periodic Table of Elements is the common long form of theperiodic table; Advanced Inorganic Chemistry by F. A Cotton and G.Wilkinson Interscience Publishers, 1962) Removal of water from producedcrude oils is termed dewatering and salt removal is termed desalting.Often, the process of dewatering also desalts the crude oil sincewater-soluble salts are removed with the water.

Dewatering the produced crude oil is desired at crude oil productionfacilities as it impacts the value of crude oil and its economictransportation. The presence of salts, especially chlorides of Group Iand Group II elements of The Periodic Table of Elements, corrode oilprocessing equipment. In order to mitigate the effects of corrosion, itis advantageous to reduce the salt concentration to the range of 1 to 5ppm or less and water content to about 0.25 to 1 wt % by weight of thecrude oil prior to transportation and processing of the oil.

Among the crude oil dewatering and/or desalting methods in use today,electrostatic separation methods are commonly used. Heavy crude oilscontaining high concentrations of asphaltenes, resins, waxes, andnapthenic acids are difficult to dewater and desalt and usually requirelonger processing times, higher process operation temperatures andhigher concentrations of demulsifier chemicals to effect the desireddewatering and desalting. As a result of these processing requirementsfor heavy crude oils the process throughput is lowered and costs fordewatering and desalting increased. Consequently, there is a need forimproved crude oil dewatering and/or desalting methods that improve theefficiency of dewatering and/or desalting especially with heavy crudeoils containing asphaltenes and naphthenic acids. The present inventionalso addresses this need.

SUMMARY OF THE INVENTION

In one embodiment is a method for separating polar hydrocarbon compoundsfrom a hydrocarbon oil containing polar hydrocarbon compounds comprisingthe steps of:

-   -   a) forming a gel in the hydrocarbon oil, and thereafter    -   b) separating the gel from the hydrocarbon oil to produce a        separated gel and a separated hydrocarbon oil.

In another embodiment is a method for dewatering and/or desalting ahydrocarbon oil containing water and salt comprising the steps of:

-   -   a) forming a gel in the hydrocarbon oil,    -   b) separating the gel from the hydrocarbon oil to produce a        separated gel and a separated hydrocarbon oil, and thereafter    -   c) separating water and salt from the separated hydrocarbon oil        to provide a dewatered and desalted hydrocarbon oil.

DETAILED DESCRIPTION OF THE PRFERRED EMBODIMENTS

The gel separation method of the instant invention is useful forhydrocarbon oils comprising polar hydrocarbon compounds. It isparticularly useful for crude oils that contain polar hydrocarboncompounds such as naphthenic acids, asphaltenes and metalloprophyrins.Separation of the polar hydrocarbon compounds from the crude oil resultsin a upgraded crude oil. Preferred hydrocarbon oils are hydrocarbon oilsselected from the group consisting of crude oil, crude oil distillate,crude oil residuum or mixtures thereof.

The desalting and/or dewatering method of the instant invention isuseful for hydrocarbon oils comprising salts, water and mixturesthereof. It is particularly useful for heavy and waxy crude oils thatare generally difficult to dewater and/or desalt. The salts present inthe hydrocarbon oil are inorganic salts including halogens, sulfates andcarbonates of Group I and Group II elements of The Periodic Table ofElements. The concentration of the salts can vary from about 0.001 to 10wt % based on the weight of the hydrocarbon oil. The process iseffective for both water-soluble and water insoluble salts that aresuspended in the hydrocarbon oil. The water content of the hydrocarbonoil-water mixture can vary in the range of 0.5 wt % to 20 wt % based onthe weight of the hydrocarbon-water mixture. The hydrocarbon oilrequired to be dewatered and/or desalted can be a crude oil, crude oildistillate, and crude oil residuum obtained from distillation ormixtures thereof. Generally the water of the hydrocarbon oil is in aform wherein the water is dispersed as droplets in the hydrocarbon oil.In this form of occurrence the hydrocarbon oil-water mixture isgenerally a water-in oil emulsion.

The gel of the invention is a complex fluid comprising hydrocarbon oil,water, water soluble salts such as sodium, potassium and calciumchlorides, water insoluble salts such as calcium carbonate and calciumsulfate, organic carbonaceous solids like coal and coke, crude oilderived compounds such as asphaltenes, naphthenic acids, naphthenicacids salts such as sodium and calcium naphthenates, organo sulfurcompounds, organo nitrogen containing compounds and metalloporphyrins.The crude oil derived compounds in the gel are polar hydrocarboncompounds, preferably surface active polar hydrocarbon compounds, andmore preferably surface active polar hydrocarbon compounds that aresurface active at a hydrocarbon-water interface. Surface activity of thepolar hydrocarbon compounds can be determined using known tensiometrictechniques such as hydrocarbon/water interfacial tension by one ofordinary skill in the art of interfacial science.

The gel has physical properties suitable for separation from thehydrocarbon oil from which it is formed. Preferably the density of thegel is greater than that of the hydrocarbon oil at the temperature themethod is conducted. More preferably the density is greater than that ofthe hydrocarbon oil and less than that of water at the temperature themethod is conducted. The density of the gel being greater than that ofthe hydrocarbon oil and less than that of water allows easy separationof the gel from the hydrocarbon oil. The gel is preferably viscoleastic.Viscoelastic properties of materials is known to one of ordinary skillin the art of rheology. By virtue of its viscoelastic nature the gel hasan elastic modulus and a viscous modulus. The elastic modulus andviscous modulus of the viscoelastic gel can be measured by one ofordinary skill in the art of fluid rheology using oscillatory visometrytechniques. Preferably the viscous modulus of the gel is at least twotimes that of the hydrocarbon oil from which it is formed at a giventemperature. Preferably the elastic modulus of the gel is at least twotimes that of the hydrocarbon oil from which it is formed at a giventemperature.

The first step of the method is to form a gel in a hydrocarbon oil. Toform the gel, a variety of methods can be employed. One non-limitingexample includes adding gel forming agents including but not limited tolignin, cellulose, coke fines, coal fines, synthetic cross linkedpolymers, cholesteryl and cholestanyl derived gellation compounds andoxidized alkyl aromatic hydrocarbons and water. Water is a preferredgel-forming agent. The amount of gel forming agent to be added can varyin the range of 0.01 to 20 wt % based on the weight of the hydrocarbonoil. When water is the gel forming agent it is preferred to add wateralso the range of 0.01 to 20 wt % based on the weight of the hydrocarbonoil. More preferrably water is in the range of 0.01 to 10 wt % based onthe weight of the hydrocarbon oil. Water addition can be in one lot orin aliquots. After addition of the gel forming agent the hydrocarbon oilis mixed and allowed to stand for a period of time and at a temperaturesufficient to promote gel formation. Mixing can be conducted during orafter addition of the gel forming agent. The preferred temperature ofaddition and mixing is in the range of about 15° C. to about 85° C. andpreferred period of time of addition and mixing is in the range of 5minutes to 10 days.

Another example of forming a gel from a hydrocarbon oil is to subjectthe hydrocarbon oil to temperature cycles i.e., increase and decreasethe temperature of the hydrocarbon oil in a temperature range severaltimes. Preferrably the temperature cycling is in the temperature rangeof 10° C. to 90° C. at atmospheric pressure and the number of cycles isat least 2 and the total time period of cycling is from 5 minutes to 10days. In another example a hydrocarbon oil is subject to pressure cyclesin a suitable pressure range. A pressure in the range of 14 psia (96.46kPa) to 150 psia (1033.5 kPa) is preferred. The hydrocarbon oil can besubject to both temperature and pressure cycles at the same time. In yetanother example the hydrocarbon oil can be subject to electrostaticfields. Preferably the electrostatic field is at potentials ranging fromabout 10,000 volts to about 40,000 volts, A.C. or D.C. Voltage gradientsin the electrostatic field range from about 500 volts per inch to about5,000 volts per inch, preferably ranging from about 500 to about 1,000volts per inch. Residence times in the electrostatic fields range fromabout 0.5 to about 120 minutes, preferably from about 0.5 to about 15minutes. In yet another example the hydrocarbon oil can be subject toshear cycling i.e., subject the hydrocarbon oil to shearing forces ofvarying intensities. This can be accomplished for example by subjectingthe hydrocarbon oil to turbulent force field followed by a quiescentforce field. The hydrocarbon oil can also be subject to sonic treatmentcycles. In this embodiment the hydrocarbon oil is subject to cycles ofultrasonic waves by turning on and turning off the ultrasonicatoralternately for a period of time sufficient to form the gel. Thetemperature, pressure, electrostatic, sonic and shear treatments can beconducted on the hydrocarbon oil or on the hydrocarbon oil treated withgel forming agents. For example, one can treat the hydrocarbon oil withwater and then subject it to the temperature, pressure, electrostatic,sonic or shear treatments to promote gel formation.

The amount of gel formed in the hydrocarbon oil is an amount sufficientto extract at least 1 weight percent of polar hydrocarbon compounds inthe starting hydrocarbon oil, preferably at least 1 weight percentsurface active polar hydrocarbon compounds, and more preferably at least1 weight percent surface active polar hydrocarbon compounds that aresurface active at a hydrocarbon-water interface. Preferably the surfaceactive polar hydrocarbon compounds are nitrogen, oxygen, sulfur andmetals containing surface active compounds of the hydrocarbon oil. Thetotal amount of polar hydrocarbon compounds of the hydrocarbon oil canbe measured by one of ordinary skill in the art of organic compoundanalyses. Preferably, the amount of gel that is formed is in the rangeof 0.5 to 20 wt % based on the initial weight of the hydrocarbon oil.More preferrably the the amount of gel that is formed is in the range of0.5 to 10 wt % based on the initial weight of the hydrocarbon oil.

The second step of the method comprises separating the gel from thehydrocarbon oil to produce a separated gel and a separated hydrocarbonoil. This separation can be accomplished by methods known to one ofordinary skill in the art of separations. The system for separation canbe considered as a liquid-viscoelastic gel system. Because of thefavorable density and viscoelastic properties of the formed gel thepreferred separation method is gravity settling followed by removal ofthe top oil phase. Centrifugation or hydrocyclone techniques can also beemployed to increase the rate of separation of the gel from the treatedoil. Suitable centrifugal force fields can be applied for theseparation. Suitable filtration methods can also be employed. Forexample, for gels formed from crude oils one can use a mineral or rockbed such as a gravel bed as a filtration medium to filter off orseparate the gel from the oil. Other filtration media such as membranefilters can also be used. After gel formation and separation, theseparated hydrocarbon oil contains polar hydrocarbon compounds that areat least 1 wt % less than the starting hydrocarbon.

The last step of the method for dewatering and desalting is separatingwater and salt from the separated hydrocarbon oil. Methods known forseparating water and salt from the hydrocarbons oils can be employed.These include methods such as electrostatic separation, centrifugationand hydrocyclone treatment. Electrostatic separation is the preferredmethod to separate the water and salts from the separated hydrocarbonoil. Preferably demulsifier chemicals known to one of ordinary skill inthe art of dewatering and desalting hydrocarbon oils are added to theseparated hydrocarbon oil and subject to electrostatic treatment toprovide the dewatered desalted oil.

The following non-limiting examples illustrate one embodiment of theinvention.

Step-1: Gel Formation

100 grams of a crude oil from Canada was used. To the crude oil wasadded 1 wt % water based on the weight of the crude oil. The crude oilwas subject to temperature cycling by heating the crude oil to 60° C.and holding the temperature at 60° C. for 30 minutes. The sample wasthen cooled to 25° C. The heating and cooling was conducted five times.The sample was then allowed to gravity settle for 5 days.

After 5 days a gel layer was observed to settle at the bottom of the jarcontaining the temperature cycled oil. The amount of gel formed was 5 wt% based on the initial weight of the crude oil. A bright light sourceheld in front or behind the jar containing the oil was sufficient todetect the gel layer.

Step-2: Separation of Oil and Gel

The oil residing on top of the gel was carefully siphoned off to providethe separated oil (denoted, sample-1). The gel was at the bottom of thejar and is the separated gel (denoted, gel sample-G). Step-3: Separationof water and salts from the separated oil (electrostatic treatment)

Two samples were examined. Sample-1 was the separated oil (obtained fromstep 2) and Sample-2 untreated Canadian crude oil. Water (5 wt %) wasadded to samples 1 and 2 and both samples shaken for 5 minutes on awrist shaker. A phenol formaldehyde ethoxylated alcohol demulsifierformulation sold by BASF Corporation as Pluradyne DB7946 was added toboth samples at a treat rate of 100 ppm based on the weight of crude oiland the mixture shaken on a wrist shaker for an additional 10 minutes.Both samples were subject to electrostatic demulsification by applying830 volts/square inch AC current to the samples at 60C for 1 hour. Aftercompletion of the procedure the samples were examined and amount ofwater separating out recorded. The samples were also analyzed for sodiumcontent by Inductively Coupled Plasma (ICP) analyses. Sample-2 did notdemulsify under the conditions of the experiment and no water wasobserved to split out at the bottom of the demulsifier vessel. InSample-1, 97% dewatering and 80% reduction in salt content was observed.Thus, formation and separation of the gel results in effectivedewatering and desalting whereas the untreated crude oil does notdemulsify under the same conditions.

Analyses of the Separated Gel

The separated gel (gel sample-G) from step 2 was subject to Theologicalanalyses using oscillatory viscometry. A Haake viscometer in theoscillating mode was used and analyses conducted at 25° C. The separatedgel (gel sample-G) had a viscous modulus of 32.5 Pascal and an elasticmodulus of 4.4 Pascal. In contrast, the separated oil (sample-2) had aviscous modulus of 7.7 Pascal an elastic modulus of 0.7 Pascal. Thus theformed gel has a significantly higher elastic and viscous moduluscompared to the crude oil.

Next, the gel phase was subject to component analysis. The gel was foundto contain 95% oil and 5% water. The oil and water from the separatedgel was analyzed. The oil of the gel (Gel Oil) was itself observed tohave a micro-concarbon residue (MCCR), naphthenic acid (TAN), basicnitrogen and sulfur level higher than the separated oil (sample-2)obtained from step-2. Additionally, the surface activity of the oil fromthe gel was an order of magnitude higher than the surface activity ofthe separated oil. This is evident in the oil/water interfacial tension{IFT (o/w)} values. Thus, in the method of the invention the gelextracts the most surface active sulfur, nitrogen and naphthenic acidcompounds. Results of the analyses are shown in Table-1. TABLE 1 Total NBasic N IFT (o/w) Oil S (%) (ppm) (ppm) TAN MCCR dynes/cm Separated Oil3.0 3800 960 0.99 6 20 Gel Oil 4.0 4700 1200 1.82 13 2

1. A method for separating polar hydrocarbon compounds from ahydrocarbon oil containing polar hydrocarbon compounds comprising thesteps of: a) forming a gel in the hydrocarbon oil, and thereafter b)separating the gel from the hydrocarbon oil to produce a separated geland a separated hydrocarbon oil.
 2. The method of claim 1 wherein saidseparated hydrocarbon oil contains said polar hydrocarbon compounds thatare at least 1 wt % less than in the hydrocarbon oil.
 3. The method ofclaim 1 wherein said gel is formed by a process selected from the groupconsisting of adding gel forming agents, subjecting to temperaturecycling, subjecting to pressure cycling, subject to shear cycling,subjecting to sonic cycling, subjecting to electrostatic fields, andcombinations thereof.
 4. The method of claim 1 wherein said separationof gel from the hydrocarbon oil in step b) is by a process selected fromthe group consisting of gravity settling, centrifugation, hydrocyclonetreatment, filtration and combinations thereof.
 5. The method of claim 1wherein said hydrocarbon oil is selected from the group consisting ofcrude oil, crude oil distillate, crude oil residuum or mixtures thereof.6. The method of claim 1 wherein said gel has a density greater than thedensity of the hydrocarbon oil at the temperature at which step b) isconducted.
 7. The method of claim 1 wherein the amount of gel formed inthe hydrocarbon oil is in the range of 0.5 to 20 wt % based on theweight of the hydrocarbon oil.
 8. The method of claim 3 wherein said gelforming agent is water.
 9. The method of claim 8 wherein said water isin the range of 0.01 to 10 wt % based on the weight of the hydrocarbonoil.
 10. The method of claim 3 wherein said temperature cycling is inthe temperature range of 10° C. to 90° C. at atmospheric pressure, thenumber of cycles is at least 2 and the total time period of cycling isfrom 5 minutes to 10 days.
 11. A method for dewatering and/or desaltinga hydrocarbon oil containing water and salt comprising the steps of: a)forming a gel in the hydrocarbon oil, b) separating the gel from thehydrocarbon oil to produce a separated gel and a separated hydrocarbonoil, and thereafter c) separating water and salt from the separatedhydrocarbon oil to provide a dewatered and desalted hydrocarbon oil. 12.The method of claim 11 wherein said gel is formed by a process selectedfrom the group consisting of adding gel forming agents, subjecting totemperature cycling, subjecting to pressure cycling, subject to shearcycling, subjecting to sonic cycling, subjecting to electrostaticfields, and combinations thereof.
 13. The method of claim 11 whereinsaid separation of gel from the hydrocarbon oil in step b) is by aprocess selected from the group consisting of gravity settling,centrifugation, hydrocyclone treatment, filtration and combinationsthereof.
 14. The method of claim 11 wherein said separation of water andsalt from the separated hydrocarbon oil in step c) is by electrostatictreatment.
 15. The method of claim 11 wherein said hydrocarbon oil isselected from the group consisting of crude oil, crude oil distillate,crude oil residuum or mixtures thereof.
 16. The method of claim 11wherein said hydrocarbon oil contains asphaltenes and naphthenic acids.17. The method of claim 11 wherein said gel is viscoleastic.
 18. Themethod of claim 11 wherein said gel has a density greater than thedensity of the hydrocarbon oil at the temperature at which step b) isconducted.
 19. The method of claim 11 wherein said gel has a densitygreater than the density of the hydrocarbon oil and lower than thedensity of water at the temperature at which step b) is conducted. 20.The method of claim 11 wherein the amount of gel formed in thehydrocarbon oil is an amount sufficient to extract at least 1 wt % ofpolar hydrocarbons compounds from the hydrocarbon oil.
 21. The method ofclaim 11 wherein the amount of gel formed in the hydrocarbon oil is inthe range of 0.5 to 20 wt % based on the weight of the hydrocarbon oil.22. The method of claim 12 wherein said gel forming agent is water. 23.The method of claim 22 wherein said water is in the range of 0.01 to 10wt % based on the weight of the hydrocarbon oil.
 24. The method of claim12 wherein said temperature cycling is in the temperature range of 10°C. to 90° C. at atmospheric pressure, the number of cycles is at least 2and the total time period of cycling is from 5 minutes to 10 days.